On the evolution of interactions between marine mesoherbivores and algae

It is suggested that the evolution of marine mesoherbivores is influenced by the effect that these animals have on the host algae, the extent of food limitation and the ultimate factors controlling diet and habitat selection. Two contrasting models are proposed to explain the evolution of mesoherbivores: coevolution and sequential evolution. From the analysis of the available information on the biology and ecology of mesoherbivores it is obvious that: (i) no generalization can be made on the impact of mesoherbivores on the host algae, (ii) food limitation in mesoherbivores may be a common event, operating through diffuse competition, (iii) mesoherbivores have the potentiality to locate and colonize any host alga present in the habitat and, (iv) host selection, and possibly diet, is subordinate to habitat selection. Considering these results altogether, it follows that we cannot support or reject either of the two proposed models. Some suggestions are made for future research that might fill in the gaps in our knowledge of the biology and ecology of mesoherbivores.